The present invention relates to a micromachine and a method of manufacturing the same, particularly to a micromachine including a vibrator electrode crossing over an output electrode, with a space portion therebetween, and a method of manufacturing the same.
Attendant on the advance of the technology of micro-processing on substrates, attention has been paid to the micromachine technology in which a micro-structure and an electrode, a semiconductor integrated circuit and the like for controlling the driving of the micro-structure are provided on a substrate such as a silicon substrate, a glass substrate, etc.
Among the micromachines, there is a micro-vibrator proposed to be utilized as a high-frequency filter for radio communication. As shown in FIG. 8, a micro-vibrator 100 includes a vibrator electrode 103 disposed over an output electrode 102a provided on a substrate 101, with a space portion A therebetween. The vibrator electrode 103 has one end portion connected to an input electrode 102b, which is constituted of the same conductive layer as the output electrode 102a. When a specified frequency voltage is impressed on the input electrode 102b, a beam (vibrating portion) 103a of the vibrator electrode 103 provided over the output electrode 102a with the space portion A therebetween is vibrated at a natural vibration frequency, whereby the capacitance of a capacitor constituted of the space portion A between the output electrode 102a and the beam (vibrating portion) 103a is varied, and the variation in capacitance is outputted from the output electrode 102a. A high-frequency filter composed of the micro-vibrator 100 having such a configuration can realize a higher Q value, as compared with high-frequency filters utilizing surface elastic wave (SAW) or thin film elastic wave (FBAR).
The micro-vibrator as above-mentioned is manufactured as follows. First, as shown in FIG. 9A, an output electrode 102a, an input electrode 102b, and a support electrode 102c which are formed of polysilicon are provided on a substrate 101 whose surface has been covered with an insulation film. These electrodes 102a to 102c are so arranged that the input electrode 102b and the support electrode 102c are disposed on the opposite sides of the output electrode 102a. Next, a sacrificing layer 105 formed of silicon oxide is provided on the substrate 101 in the state of covering the electrodes 102a to 102c. 
Subsequently, as shown in FIG. 9B, the sacrificing layer 105 is provided with connection holes 105b and 105c reaching the input electrode 102b and the support electrode 102c, respectively. Thereafter, a polysilicon layer 106 is provided on the upper side of the sacrificing layer 105, inclusive of the inside of the connection holes 105b and 105c. 
Next, as shown in FIG. 9C, the polysilicon layer 106 is patterningly etched, to form a belt-like vibrator electrode 103 extending over the output electrode 102a. In this case, in order to prevent the input electrode 102b and the support electrode 102c formed of polysilicon from being etched, the polysilicon layer 106 is patterningly etched so that the connection holes 105b and 105c are entirely covered.
Thereafter, the sacrificing layer 105 is selectively removed, to form the space portion A between the output electrode 102a and the vibrator electrode 103, thereby completing the micro-vibrator 100, as shown in FIGS. 9A to 9C.
FIG. 10 is a diagram showing the relationship between the length (beam length) L of the beam (vibrating portion) 103a of the micro-vibrator 100 configured as above and the natural vibration frequency. As shown in the diagram, the theoretical natural vibration frequency (Theory) based on the following formula (1) is proportional to (1/L2). Therefore, in order to achieve a higher frequency, it is necessary to reduce the beam length L.
                              f          R                =                                            0.162              ⁢              h                                      L              2                                ⁢                                    EK              ρ                                                          (        1        )            where h is film thickness, E is Young's modulus, K is electromagnetic coupling factor, and ρ is film density.
In the above-mentioned micro-vibrator 100, however, since the space portion A and the vibrator electrode 103 are so provided as to bridge over the output electrode 102a, it is impossible to set the beam length L smaller than the line width of the output electrode 102a. 
In addition, where it is intended to miniaturize the beam length L in order to obtain a higher frequency, it is necessary to miniaturize also the line width of the output electrode 102a, so that the capacitance between the output electrode 102a and the vibrator electrode 103 is reduced, resulting in a lower output. The above-mentioned points constitute factors which restrict the achievement of a higher frequency through miniaturizing the beam length L.
Accordingly, it is an object of the present invention to provide a micromachine including a vibrator electrode which promises a further advance in achieving a higher frequency through miniaturization of beam length, and a method of manufacturing the same.